The present invention provides a ground proximity warning system and method for rotary wing aircraft such as helicopters, gyrocopters, and tilt rotors and more particularly to logic and displays useful in a helicopter enhanced ground proximity warning system, or EGPWS.
Ground proximity warning systems, or GPWS, provide aural and visual warnings of conditions when the aircraft is in potentially hazardous proximity to terrain, and/or in a flight condition apparently inappropriate given the aircraft""s position relative to terrain. Earlier generation ground proximity warning systems sensed dangerous approach to terrain by using a radar altimeter to sense height above the ground. The rate at which height above ground changes, is compared with a predefined envelope(s) to determine if a dangerous condition exists. Classic GPWS systems also contain additional alert functions called xe2x80x98modesxe2x80x99 that alert to other potentially hazardous conditions based on flight regime. Examples of GPWS devices are contained in U.S. Pat. Nos. 3,715,718; 3,936,796; 3,958,218; 3,944,968; 3,947,808; 3,947,810; 3,934,221; 3,958,219; 3,925,751; 3,934,222; 4,060,793; 4,030,065; 4,215,334; and 4,319,218.
Later generation GPWS devices, called EGPWS devices or terrain awareness systems (TAWS), include a stored terrain database that compares the position of the aircraft in three dimensional space with the stored terrain information to identify potential conflicts. EGPWS devices may also include all the functionality and modes of the classic GPWS devices. Examples of EGPWS-type devices include U.S. Pat. Nos. 4,646,244; 5,839,080; 5,414,631; 5,448,563; 5,661,486; 4,224,669; 6,088,634; 6,092,009; 6,122,570 and 6,138,060.
In certain EGPWS designs, the position of the terrain relative to the aircraft may be shown on a display in the cockpit. In some displays, the terrain is color-coded according to the degree of hazard. For example, green colored terrain usually depicts nonhazardous terrain below the aircraft. Yellow colored terrain usually depicts terrain that is in proximity to the aircraft and/or which may cause the ground proximity system to generate a precautionary alert. Red colored terrain usually depicts terrain at or above the aircraft altitude or for which the ground proximity warning system will issue a warning from which evasive action must be taken. U.S. Pat. Nos. 5,839,080 and 6,138,060 describe some terrain cockpit displays. U.S. Pat. No. 5,936,522 describes a terrain display having vertical and plan views.
The above referenced systems have been primarily developed for fixed wing aircraft. Rotary wing aircraft and aircraft capable of hover present unique challenges for ground proximity alerting due to the different flight profiles flown and the unique capabilities of rotary wing aircraft. For example, unlike fixed wing aircraft, rotary wing aircraft can cease all forward motion while still remaining airborne. Rotary wing aircraft can also descend straight down from a hover to land on all sorts of terrain, and need not make a gradual descent and approach to land as in the case of fixed wing aircraft.
U.S. Pat. No. 5,781,126 titled xe2x80x9cGround Proximity Warning System and Methods for Rotary Wing Aircraft;xe2x80x9d U.S. Pat. No. 5,666,110 titled xe2x80x9cHelicopter Enhanced Descent After Take-off Warning for GPWS;xe2x80x9d and U.S. Pat. No. 6,043,759 titled xe2x80x9cAir Ground Logic System and Method for Rotary Wing Aircraft;xe2x80x9d and co-pending application Ser. No. 08/844,116 titled: xe2x80x9cSystems and Methods for Generating Altitude Callouts for Rotary Wing Aircraft,xe2x80x9d each address various issues associated with applying ground proximity warning technology to rotary wing aircraft and are each incorporated herein by reference. These patents are applicable to both conventional and enhanced ground proximity warning designs for use in helicopters, however, these patents address the particularities of modifying various of the xe2x80x9cmodesxe2x80x9d for use in helicopters. Specifically, U.S. Pat. No. 5,781,126 includes a barometric altitude rate detector including a controller for adjusting this rate detector to account for downwash of the rotary wing. U.S. Pat. No. 5,666,110 discloses a descent after take-off protection envelope. U.S. Pat. No. 6, 043,759 discloses a logic method and device for determining when the helicopter is in the airborne or ground state which assists with preventing nuisance alarms during helicopter autorotations. Ser. No. 08/844,116 discloses a device and method for generating altitude call outs during helicopter landing operations.
None of the above mentioned patents account for modifying the terrain look ahead logic or the associated terrain display of an EGPWS type device to account for the unique flying performance of helicopters and other rotary wing craft.
The present invention recognizes the problems in enhanced ground proximity alerting for rotary wing aircraft such as, for example, helicopters, gyrocopters and tilt rotors when in the rotor mode, hereinafter generically and interchangeably referred to as xe2x80x9chelicopter(s)xe2x80x9d or xe2x80x9crotary wing aircraftxe2x80x9d. In particular, the present invention recognizes that certain categories of aircraft such as rotary wing aircraft and airships are capable of executing an avoidance maneuver by coming to a stop in a hover. The present invention further recognizes that the terrain threats as depicted on the display should preferably also be modified to reflect the unique, yet normal operating capabilities of such aircraft. In addition, the present invention recognizes the unique landing characteristics of rotary wing aircraft.
According to one aspect of the present invention, a helicopter EGPWS uses a look ahead distance to define terrain that is a threat to the aircraft. If terrain is located within the boundaries of the warning envelope, an alert is given to the pilot. In a preferred embodiment of the present invention, this look ahead distance is based upon the nominal distance required to halt forward momentum and enter a hover.
According to another aspect of the present invention, a helicopter EGPWS permits the helicopter to land at any location, including off-airport locations, without incurring nuisance alarms. In a preferred embodiment of the invention, the helicopter EGPWS uses groundspeed in conjunction with helicopter vertical speed to define a terrain floor below which a proximity warning will be given. In this manner, the helicopter executing a safe landing, for example, on a hillside will not incur an unwanted terrain proximity alert.
According to yet another aspect of the present invention, the present invention recognizes that a display color coded to alert pilots of fixed wing aircraft to potential hazards may result in displaying non-threatening terrain as a hazard to pilots of rotary wing aircraft. The EGPWS and EGPWS display of the present invention color codes terrain based upon flight regimes associated with modes of operation typical for rotary wing aircraft.
Further details and operation of the present invention will be described below with reference to the drawings.